For decades, individuals under house arrest or parole have been required to wear an ankle monitor (also known as a tether, or ankle bracelet), which is a homing device that sends a radio frequency signal containing location and other information to a receiver, at timed intervals. If an offender moves outside of an allowed range, law enforcement is notified. Ankle monitors are designed to be tamper-resistant and can alert law enforcement to removal attempts.
Many believe that requiring a criminal, who has been released from prison, to wear a GPS bracelet, is essential for law enforcement to keep track of such individuals, and is a tool for the prevention repeat crimes from being committed. Accordingly, some states have passed laws, which required round-the-clock GPS monitoring of serious sex offenders for life.
Typically, the GPS systems involve an ankle monitor designed to stay within a specified distance of a GPS transmitter, which is in communication with a satellite that then transmits location information over cellular networks to a central computer. Such systems are designed to send an alert if an offender tries to remove the device or enter a forbidden area, such as, for example, a school or park, a liquor store, or near a victim's residence. However, the alerts go out for a variety of routine reasons, such as, for example, GPS signals blocked by buildings, dead batteries, cracked cases, loose straps, which can overwhelm law enforcement with volumes of false positives. Since, many technological problems exist with current GPS monitoring systems, new methods and systems for providing online monitoring of released criminals are needed.